Field of the Invention
This invention relates to a nucleic acid sequence encoding a functional module or domain of a particular peptidoglycan hydrolase, i.e., the Phage Twort (PlyTW) endolysin, a protein which specifically attacks the cell wall peptidoglycan of untreated Staphylococcus aureus. The PlyTW endolysin is active over a broad range of physiological conditions including the pH and calcium concentration of bovine milk. The invention further relates to methods of treating diseases caused by the bacteria for which the PlyTW endolysin is specific.
Description of the Relevant Art
Global increases in antibiotic resistant pathogens have led to a renewed search for novel antimicrobials. One highly resistant bacterium, Staphylococcus aureus, has a high negative impact worldwide on the health of humans (Klevens et al. 2007. JAMA 298:1763-1771; WHO. 2014. In: Antimicrobial Resistance: Global Report on Surveillance, World Health Organization, Geneva, Switzerland), livestock (bovine, porcine, equine and poultry (Price et al. 2012. M. Bio. 3:e00305-e00311) and companion animals (dogs, cats, and horses) (Davis et al. 2014. Lett. Appl. Microbiol. 59:1-8; Harrison et al. 2014. M. Bio. 3:e00985-e0013). Recent estimates place S. aureus identified in hospitals at 70% resistant to methicillin, i.e., methicillin-resistant S. aureus (MRSA; Taubes, G. 2008. Science 321:356-361). Methicillin-resistant isolates, at lower frequencies, have been found in bovine mastitis isolates (Brody et al. 2008. PLoS ONE 3:e3074; Turutoglu et al. 2009. Vet. Res. Commun. 33:945-956; Alves et al. 2009. Vet. Microbiol. 137:190-195). Alternative antibiotic treatments, such as vancomycin in human infections, are rapidly losing efficacy as resistant strains are emerging, e.g., thirteen cases of vancomycin-resistant S. aureus, VRSA, have occurred in the United States since 2002 (CDC. 2013. In: Antibiotic Resistance Threats in the United States 2013. CDC, Atlanta). With increasing numbers of antibiotics proving to be ineffective, novel antibiotics are necessary to combat this emerging threat. Bacteriophage endolysins are a source of novel fusion antimicrobials that are uniquely poised to treat infections that are refractory to conventional antibiotic treatment (Donovan et al. 2009. Biotech. International 21:6-10).
Bacteriophage endolysins are peptidoglycan hydrolase enzymes encoded by bacteriophage (viruses that infect bacteria) to degrade the peptidoglycan component of the bacterial cell wall and thus allow nascent phage particles to escape the host cell (for review: Fischetti, V. A. 2008. Curr. Opin. Microbiol. 11:393-400; Donovan, D. M. 2007. Recent Patents in BioTechnology 1:113-122; Loessner, M. J. 2005. Curr. Opin. Microbiol. 8:480-487; Fischetti, V. A. 2010. Int. J. Med. Microbiol. 300:357-4362; Nelson et al. 2012. Adv. Virus Res. 83:299-365; Shen et al. 2012. In: Bacteriophages in Health and Disease, Hyman and Abedon, Eds., CABI, Wallingford, UK, pp. 217-239.) Endolysins can harbor any of three unique activities: endopeptidase, amidase (Becker et al. 2009a. FEMS Microbiol. Lett. 294:52-60 Navarre et al. 1999. J. Biol. Chem. 274:15847-15856) or glycosidase activity (Pritchard et al. 2007. Appl. Environ. Microbiol. 73:7150-7154) (for review see Loessner, M. J. 2005, supra). The exact amino acid sequence and composition of the Gram positive peptidoglycan can vary between genera or even between species within a genus (Schleifer and Kandler. 1972. Bacteriol. Rev. 36:407-477). The near-species specificity of the Gram positive peptidoglycan structure and the specificity of the endolysin domains distinguish these enzymes as potential narrow spectrum antimicrobials.
Thus, because of the rise of drug resistant pathogenic bacteria, there is a need for new pathogen-specific antimicrobial treatments. Reagents that are specific for the genera, species or strains of concern and that are also refractory to resistance development are important for effective control of disease and therapeutic treatments.